1. Field of the Invention
The present invention relates to a ceramic electronic component and a method for manufacturing the ceramic electronic component, and more particularly, the present invention relates to a ceramic electronic component in which an electrode such as an external terminal electrode on a component main body includes a plating film formed by plating, and a method for manufacturing the ceramic electronic component.
2. Description of the Related Art
As shown in FIG. 7, a laminate-type ceramic electronic component 101 typified by a laminated ceramic capacitor typically includes a component main body 105 which has a stack structure including a plurality of stacked ceramic layers 102 of, for example, a dielectric ceramic, and a plurality of layered internal electrodes 103 and 104 formed along the interfaces between the ceramic layers 102. The plurality of internal electrodes 103 and the plurality of internal electrodes 104 each have ends respectively exposed at one and the other end surfaces 106 and 107 of the component main body 105, and external terminal electrodes 108 and 109 are formed respectively so as to electrically connect the respective ends of the internal electrodes 103 to each other and the respective ends of the internal electrodes 104 to each other.
For the formation of the external terminal electrodes 108 and 109, typically, a metal paste containing a metal constituent and a glass constituent is applied onto the end surfaces 106 and 107 of the component main body 105, and then subjected to firing, thereby first forming paste electrode films 110. Next, a first plating film 111 containing, for example, nickel as its main constituent is formed on the paste electrode films 110, and a second plating film 112 containing, for example, tin or gold as its main constituent is further formed thereon. More specifically, the external terminal electrodes 108 and 109 are each constituted of a three-layer structure of the paste electrode film 110, the first plating film 111, and the second plating film 112.
The external terminal electrodes 108 and 109 are required to provide favorable solderability when the laminate-type ceramic electronic component 101 is mounted onto a substrate with the use of solder. At the same time, the external terminal electrode 108 is required to serve to electrically connect the plurality of internal electrodes 103 to each other, which are electrically insulated from each other, and the external terminal electrode 109 is required to serve to electrically connect the plurality of internal electrodes 104 to each other, which are electrically insulated from each other. The second plating film 112 described above serves to ensure solderability, whereas the paste electrode film 110 serves to electrically connect the internal electrodes 103 to each other and the internal electrodes 104 to each other. The first plating film 111 serves to prevent solder erosion in the solder joint.
However, the paste electrode film 110 has a large thickness of several tens of μm to several hundreds of μm. Therefore, in order to limit the dimensions of the laminate-type electronic component 101 up to certain specifications, there is undesirably a need to reduce the effective volume for ensuring a capacitance because there is a need to ensure the paste electrode layers 110 in terms of volume. On the other hand, the plating films 111 and 112 each have a thickness on the order of several μm. Thus, if the external terminal electrodes 108 and 109 can be constituted only of the first plating film 111 and the second plating film 112, the effective volume can be ensured more for ensuring the capacitance.
For example, Japanese Patent Application Laid-Open No. 2004-146401 discloses a method in which a conductive paste is applied to at least ridge sections of edge surfaces of a laminate (component main body) along the stacking direction of internal electrodes so as to come into contact with leading sections of the internal electrodes, and the conductive paste is subjected to firing or thermal curing to form a conductive film, and further, the edge surfaces of the laminate are subjected to electroplating, thereby forming an electroplating film so as to be connected to the conductive film on the ridge sections described above. According to this method, the external terminal electrodes on the edge surfaces can be reduced in thickness.
In addition, Japanese Patent Application Laid-Open No. 63-169014 discloses a method in which an electroless plating film is formed on the entire sidewall surface of a component main body, at which internal electrodes are exposed, so as to short circuit the internal electrodes exposed at the sidewall surface. According to this method, the external terminal electrodes can also be reduced in thickness.
The plating film described above is basically formed by growing a plated deposit that is deposited while using, as starting points, exposed sections of the internal electrodes as conductors, so as to provide a substantially uniform thickness on the ceramic section. More specifically, plating growth in a direction parallel to a surface to be plated is used for the formation of the plating film.
Therefore, when a plating film is also desired to grow efficiently in a location with no exposed sections of internal electrodes, such as a ridge-line section of a component main body, there is typically a need to form in advance a conductive film to serve as a base for the plating film, as described also in Japanese Patent Application Laid-Open No. 2004-146401 mentioned above. However, the formation of the conductive film to serve as a base leads to an increase in cost or an increase in the number of steps.
In order to solve this problem, a method has been also considered in which, in the formation of a plating film, the plating condition is set so as to provide considerably high plating growth to allow for plating growth directly onto the surface of the ceramic section. However, the condition for higher plating growth rather has difficulty with controlling plating growth, and has difficulty with placing an end edge of the plating film in a predetermined position.
On the other hand, the disclosure of, for example, Japanese Patent Application Laid-Open No. 2004-15016, has been attracting attention as a method which allows the control of plating growth described above. Japanese Patent Application Laid-Open No. 2004-15016 discloses a technique for plating onto a surface of an external terminal electrode after the formation of the external terminal electrode by firing onto a component main body in a method for producing a chip-type electronic component such as a laminated chip thermistor, rather than a technique for forming a plating film directly onto a surface of a component main body.
In the case of the thermistor as described in Japanese Patent Application Laid-Open No. 2004-15016, the component main body is configured with the use of a semiconductor ceramic, and thus has a relatively low surface resistance. Therefore, the thermistor has a problem that plating growth is likely to be caused on an undesired location of the component main body.
In order to solve this problem, Japanese Patent Application Laid-Open No. 2004-15016 discloses several techniques, and to make an explanation, for example, with reference to FIG. 7, discloses the formation of a glass layer 113 on a section of the surface of the component main body 105 without the external terminal electrodes 108 and 109 being formed, and the formation of a water repellent layer 114 thereon which is of a titanate coupling agent, as indicated by a dashed line. Japanese Patent Application Laid-Open No. 2004-15016 also discloses an example of forming only the water repellent layer 114 without the formation of the glass layer 113.
The glass layer and the water repellent layer described above are effective for preventing undesired plating growth. However, the techniques disclosed in Japanese Patent Application Laid-Open No. 2004-15016 have the following problems.
First, in each case of the glass layer and the water repellent layer, it is difficult to form these layers without variation in a desired location such as a location with no external terminal electrode formed, when a coating step or an immersion step is required for the formation of these layers. This difficulty makes the control of plating growth difficult.
In addition, in the case of the glass layer, the layer may have the property of being easily dissolved in a plating solution. Therefore, when the technique disclosed in Japanese Patent Application Laid-Open No. 2004-15016 is diverted to a technique for forming a plating film directly onto a surface of a component main body, the glass layer may be partially dissolved in a plating solution to cause undesired plating growth. While it may be possible to use a plating solution which never causes this problem, the degree of freedom for the design of the plating bath will be decreased in this case.
In addition, when a water repellent agent is used in the technique for forming a plating film directly onto a surface of a component main body, there is an increased concern that plating growth may also be inhibited in a location requiring plating growth. Therefore, this case also makes the control of plating growth difficult.